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Experimental results and analysis of sparse microwave imaging from spaceborne radar raw data SCIENCE CHINA Information Sciences 55, 1801 (2012); Influence factors of sparse microwave imaging radar system performance: approaches to waveform design and platform motion analysis SCIENCE CHINA Information Sciences 55, 2301 (2012); Coherent processing for ISAR imaging with sparse apertures SCIENCE CHINA Information Sciences 55, 1898 (2012); Sparse synthetic aperture radar imaging with optimized azimuthal aperture SCIENCE CHINA Information Sciences 55, 1852 (2012);. REVIEW .

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The LIGO detection of gravitational waves (GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes (AST3), located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter. We report optical observations of the GW source (GW 170817) in the nearby galaxy NGC 4993 using AST3. The data show a rapidly fading transient at around 1 day after the GW trigger, with the i-band magnitude declining from 17.23 ± 0.13 magnitude to 17.72 ± 0.09 magnitude in ∼ 1.8 hour. The brightness and time evolution of the optical transient associated with GW 170817 are broadly consistent with the predictions of models involving merging binary neutron stars. We infer from our data that the merging process ejected about ∼ 10 −2 solar mass of radioactive material at a speed of up to 30% the speed of light.

In a conventional synthetic aperture radar (SAR) image, a moving target may be smeared and displaced. Taking direct action on the defocused region of interest (ROI) data from the result of a conventional imaging algorithm, this paper presents an imaging method of the ground moving target in high-resolution SAR. A 2-D equivalent velocity parameter space is built along the azimuth and range directions with the derivation of an exact analytic expression of the ROI. In each pair of equivalent velocity parameters, the Stolt interpolation is used herein to remove the residual phase error. After that, a graph of the ROI complex subimage contrast is produced with respect to the equivalent velocity parameter space. Based on the maximum contrast principle, the desired equivalent velocity is then estimated and applied for deblurring the ROI. Finally, we can achieve the refocused SAR image of the moving target. Different from the conventional approach of moving target autofocusing that requires resynthesizing back to the full data from the cropped ROI data, the proposed method directly operates on the small-sized defocused ROI subimage without any resynthesizing operations. It is helpful for the computational burden reduction, procedure simplification, and clutter interference suppression. The experiments on synthetic and real data are carried out to validate the effectiveness of the proposed method. Index Terms-Ground moving target, region of interest (ROI), synthetic aperture radar (SAR). 0196-2892

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With the increasing threat of terrorism in recent years, the detection of concealed weapons, plastic bombs and other contraband at secure locations attracts more and more countries' attention all over the world. Three-dimensional (3D) microwave imaging surveillance systems, allowing for acquisition of full 3D microwave images of human body, have been developed for security applications. In this paper, we firstly propose a 3D imaging algorithm which not only accounts for the free space propagation losses and wavefront curvature but also avoids 3D interpolation in the 3D wavenumber domain without suffering from any approximations and truncation errors. Then, the sampling constraints and the resolution issues associated with proper and alias-free implementation of the 3D reconstruction are analyzed. Finally, the focusing capabilities of our proposed imaging algorithm are investigated and verified by means of numerical simulations as well as theoretical analysis, and an approach for better displaying projected images is examined.